1. Field of the Invention
This invention relates to explosive devices and to boring and penetrating the earth. More specifically, the invention relates to well-treating apparatus for increasing the flow rate in oil or gas recovery operations.
2. Description of the Prior Art
Oil and gas recovery from a given strata requires that the strata be permeable, allowing oil or gas from remote areas to migrate toward the well. It is known in the art that recovery levels are often reduced because of well fouling caused by foreign matter, sedimentation, or paraffin build-up near the well bore. A commonly used technique that restores greater flow rate of the oil or gas is to fracture the mineral bearing formation, thereby increasing the effective permeability of the strata and creating clear passages for flow of the mineral.
Known methods of fracturing the mineral bearing formation include hydrofracing and the use of explosives, the advantages and the problems of which are well known in the art, as described in U.S. Pat. No. 3,762,326 to Edgell teaching the use of controlled directional charges between opposing pancake charges and acting on a liquid to fracture a formation. Edgell teaches the use of shaped charges capable of directing the force of the explosion in a controlled direction, using the "Monroe Principle". Experimental work with controlled directional charges of the kind disclosed in the Edgell patent reveals that the fracturing efficiency of this kind of charge can be substantially increased through certain structural changes, which are the subject of the present disclosure.
A number of different configurations of shaped charges are known in the prior art. U.S. Pat. No. 3,013,491 to Poulter teaches the use of radially directed conical charges to perforate well casings. U.S. Pat. No. 2,935,020 to Howard teaches the use of axially and circumferentially directed charges to cut windows in well casing. Other shape variations are taught in U.S. Pat. No. 2,831,429 to Moore. Thus, the cutting of longitudinal slots, circular perforations, or windows through the use of shaped charges that utilize the Monroe Principle is well known in the prior art. In operation, a shaped charge such as a conical charge having a V-shaped inner face detonates from the apex of the V and directs the explosive force in a jet that exits the open end of the V and exerts its force over a relatively narrow target area.